Three ongoing projects are described in this continuation application: 1) ANTIBODY PROJECT: Ring-shaped complexes formed between antibody molecules and bivalent hapten are employed to study the mechanism of complement activation. Electron micrographs of Clr2Cls2 have been obtained, and we are examining the structure of this molecule and its possible mode of interaction with the ring-shaped antibody complexes. 2) CHROMATIN PROJECT: The stability of nucleosomes to extremes of ionic strength and pH is being examined. We find that there is a release of DNA from the nucleosome above pH 9.5. We are measuring the titration behavior of nucleosomes over the entire pH range but especially on the alkaline side where release of DNA occurs. Also, we are studying the salt-induced transfer of nucleosomes between various DNA, and propose to examine that which occurs between procaryotic and eucaryotic DNA. 3) LIPOPROTEIN PROJECT: We are studying triglyceride-rich lipoproteins which have an elevated content of saturated triglycerides. These VLDL exhibit a phase transition at approximately 50 degrees C where the saturated triglycerides melt. We believe that they exist in a fluid but supersaturated state in serum, and that they freeze when isolated at room temperature.